The present invention relates generally to an electrically controlled fuel injection system of an internal combustion engine, and more particularly to an arrangement for use with the system for improving reliability of engine operation.
It is well known to employ an electrically controlled fuel injection system in order to increase engine performance of a vehicle and to reduce harmful exhaust emission etc. The conventional control system usually comprises a computer, an air flow meter, an electrical switch operatively coupled to a throttle, and a distributor. The computer is electrically connected to the air flow meter for deriving therefrom an information indicative of the amount of air flowing through the manifold and also connected to the distributor for sensing the ignition timing. The control system electrically controls, on the basis of the informations thus obtained, the fuel injection timing and also the quantity of fuel to be injected into cylinders of the engine through injection valves provided in respective manifold branches. In the above-mentioned control system, it is of usual practice that the system is designed in such a manner as to cease the fuel injection for an economical purpose and reduction of harmful exhaust emission while the vehicle runs by inertia, i.e., free-wheels, that is, when the engine speed is above a predetermined value (for example, 1300 rpm) and at the same time the degree of opening of the throttle is below a predetermined value (for example, an angle of 3.degree. while idling). In the above, the engine speed is sensed from the distributor by the computer.
In the aforementioned conventional control system, however, there are encountered some difficulties as to the ceasing of the fuel injection. That is, in the case that the control system ceases the fuel injection upon the detection of the engine speed exceeding the predetermined level, when thereafter, the engine speed in turn falls down below the predetermined level, there might be a possibility that the engine stops due to delayed fuel supply resulting from slow response to the change of the engine speed. This possibility is especially considerable in a vehicle equipped with automatic transmission, wherein, it its inertia or free-wheeling run, the engine speed is scarcely affected by the driving wheels. Furthermore, the above-mentioned possibility also tends to occur in the case where a driver accelerates the engine when the vehicle is at rest and immediately thereafter changes the transmission from neutral to a drive range.
To avoid these inherent defects of the prior art, in accordance with the present invention, there are provided two electrical switches which are connected in series with each other. One of these two switches is operatively connected to a transmission shift lever such as to open in response to the neutral position of the shift lever thus breaking a circuit applying information to the computer indicative of the ceasing of fuel injection. On the other hand, the other switch is operatively connected to a vehicle speedometer such as to open in response to the vehicle speed below a predetermined level (for example, 10 kph) to function as the firstly mentioned switch.